When A Patient Presents With A Pruritic Lower Extremity Rash

A 50-year-old female presented to the office with the chief complaint of an itching rash on her ankles and feet. She reported the itch to be severe at times. The duration of symptoms was for at least a few months.

The patient had no prior treatment for the condition. She denied any known cause for it. She denied any new medications, activities, recent traveling or new detergents for laundering her clothes. I asked her if she any rashes elsewhere on her body and she did have a similar rash on the flexor surface of her wrists.

Her past medical history was remarkable for asthma, diabetes mellitus, gastroesophageal reflux disease and dyslipidemia. Her current medications included insulin, glipizide (Glucotrol, Pfizer) and simvastatin.

In terms of the patient’s social history, she is married, a non-smoker and only has a mild history of alcohol use. She currently works for the United States Postal Service as a teller in a local branch.

In regard to the physical examination, her vascular status was remarkable for palpable pedal pulses with brisk capillary refill to the toes. She had normal deep tendon reflexes and no loss of epicritic sensation after testing with a Semmes-Weinstein 5.07 g monofilament. The orthopedic exam revealed symmetric, pain-free range of motion of the ankle, subtalar and midtarsal joints. The dermatologic exam revealed a rash on her ankles and feet. The rash is a cluster of purple-colored plaques with fine scales in a symmetrical fashion on her ankles and wrists.

Key Questions To Consider

1. What is the most likely diagnosis?
2. What is the differential diagnosis?
3. What are the key characteristics of this condition?
4. What is the treatment?

Answering The Key Diagnostic Questions

1. The most likely diagnosis is lichen planus.
2. The differential diagnoses include psoriasis, pityriasis rosea, pityriasis rubra pilaris, granuloma annulare and discoid lupus.
3. The key characteristics include a violaceous plaque and a planar (flat topped) appearance with a fine scale. The scale has a characteristic appearance of gray to white streaks known as Wickham’s striae.
4. Treatment is generally with high potency topical steroids such as clobetasol.

Psoriasis is an autoimmune disorder of the skin. Plaque psoriasis is a main differential in this case. Plaque psoriasis is characterized by a silvery scale on an erythematous plaque. Itching can be severe with psoriasis. The most common areas of the body in which psoriasis occurs include the scalp, elbows, knees and back. There can be excoriations and crusting of the primary lesion.

Pityriasis rosea most commonly occurs in young adults and children. The primary lesion is a rose- to fawn-colored plaque in oval shape. The location of pityriasis rosea is usually the trunk. In the classic presentation of pityriasis rosea, a primary lesion will occur followed by satellite lesions one to two weeks later. This is called a herald patch.

Pityriasis rubra pilaris is a rare condition affecting the palms and soles. It occurs in children and adults. There is yellowing hyperkeratotic skin with red to orange colored scaling plaques.

Eczema and dermatitis occur commonly in a podiatric practice. It is easy to get in a rut and make the diagnosis of eczema when a patient presents with a scaling rash. Eczema generally describes a chronic condition whereas one would use dermatitis to describe an acute scenario. Nummular eczema is a type of atopic dermatitis. Its appearance is a “coin-shaped” plaque with a scale. The color is usually skin colored or pink. There may be a past history of eczema, asthma and hay fever. These patients tend to have sensitivities and multiple allergies.

Discoid lupus erythematosus is an autoimmune disease of the skin. This is the milder form of systemic lupus erythematosus, which affects all organ systems of the body. There is no known cause of lupus. Young Hispanic and African-American women are more likely to be affected with this condition. The rash associated with discoid lupus includes a red-colored plaque with or without a scale. The lesions may turn darker at the periphery to appear brown or purple in color. The center of the lesion may become white and scarred in appearance.

Granuloma annulare is another pink or skin-colored plaque that occurs over joints of the fingers, elbows, around the knees and on the dorsal foot. These lesions are more likely to affect children or young adults although they can occur in anybody regardless of age. Typically with these lesions, one will note a cluster of raised bumps or nodules in a circular fashion. At times, it will leave an indented center. Generally speaking, there is only mild itching and sometimes there are no symptoms other than the rash itself.

Keys To Treating Lichen Planus

This patient had a well-demarcated, purple-colored plaque with itching and scaling. Most of the eczematous rashes are pink, red or flesh-colored. Moreover, eczematous lesions tend to have small blisters, become wet and may fissure.

The correct diagnosis in this case report is lichen planus, which is described as a violaceous plaque with a planar (flat topped) appearance and a fine scale. The scale has a characteristic appearance of gray to white streaks known as Wickham’s striae. Lichen planus can occur in mucous membranes such as the mouth and genitals. The most common areas of the body that lichen planus affects include the wrist and ankle. Lichen planus can also cause nail disease including thickening, longitudinal ridging, splitting and pterygium.

The key to the diagnosis in this case was the well-demarcated purple colored plaque with Wickham’s striae. Moreover, the lesions were on both ankles and wrists, which is a classic presentation. Remember, lichen planus rarely has any crusts, excoriations, vesicles or wetness.

Lichen planus is thought to be a cell-mediated autoimmune disorder against keratinocytes. Certain drugs can induce lichen planus. This is called a lichenoid drug eruption. The most common drugs associated with this include beta-blockers, nonsteroidal anti-inflammatory drugs, angiotensin-converting enzyme (ACE) inhibitors, gold, sulfonylureas, penicillamine, anti-malarial drugs and thiazides. Systemic conditions that may cause lichen planus include diseases of the liver such as hepatitis and cirrhosis.

The onset of lichen planus may be gradual or abrupt. Sites of minor injury may cause the lesion to erupt. This is known as the Koebner phenomenon. The oral mucosa is involved in about 50 percent of the cases. Nails are involved in 10 percent of cases.

Treatment of lichen planus is generally with high potency topical steroids such as clobetasol when it is on the thicker skin of the foot. Areas of thinner skin such as the leg may require less potent steroids such as triamcinolone. For resistant cases, one can use intralesional injections of triamcinolone acetate. When there are widespread rashes, a course of oral prednisone may be beneficial. Often, the lesions are self-limiting and resolve without treatment.

Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is in private practice in Phoenix. Dr. Fishco is also a faculty member of the Podiatry Institute.